When the Aurora 8B/10B core receives a UFC message, it passes the data to the user application through a dedicated UFC AXI4-Stream interface. The data is presented on the m_axi_ufc_rx_tdata port; m_axi_ufc_rx_tvalid indicates the start of the message data and m_axi_ufc_rx_tlast indicates the end. m_axi_ufc_rx_tkeep is used to show the number of valid bytes on m_axi_ufc_rx_tdata during the last cycle of the message.